The hardware functionality of Arduino can be extended with
external plug-ins referred as shields (http://shieldlist.org) commercially
manufactured or created by the user. The functions
of shields include for example adding networking capabilities
such as ethernet (http://arduino.cc/en/Main/ArduinoEthernet
Shield), Bluetooth (http://iteadstudio.com), ZigBee (http:
//arduino.cc/it/Main/ArduinoXbeeShield); TFT touch panel
capability (http://www.adafruit.com/products/376); data logging
capability without the need of a computer (http://www.
ladyada.net/make/logshield); joystick and button combination
for reading user input (http://www.sparkfun.com/products/
9760); motor drive shields (http://arduino.cc/en/Main/Arduino